Chiral water-soluble pyridyl porphyrins: Design, synthesis, characterization and applications

Cationic metalloporphyrins have a wide range of applications as water-soluble oxidation catalysts and as hosts for recognition of small molecules in water. Chiral versions of these porphyrins can have potential applications as catalysts for enantioselective epoxidation of unfunctionalized olefins and as hosts for chiral recognition of small molecules, such as amino acids in water.; Novel chiral water-soluble porphyrins were designed keeping in mind catalyst stability. Chiral hydrophobic clefts and pockets were incorporated in the designs to stabilize the organic substrate and provide chiral induction. The tetraalkylation of meso-tetrakis(2-pyridyl)porphyrin (2-PyP) with (R)-(+)-bomylbromoacetamide was carried out successfully, to provide a mixture of atropisomers. The HPLC separation and characterization of the atropisomers of this porphyrin and of other tetraalkylated products obtained by alkylation of 2-PyP with bromoacetamides were explored in detail. In all of these cases, the preferential formation of a single atropisomer as the major product was observed. HPLC conditions for the separation of the partially alkylated products formed during the course of the reaction were also developed. This gave us the opportunity to study the progress of these reactions by monitoring the formation and further reaction of the partially alkylated products, as well as provide an explanation for the observed selectivity in alkylation of 2-PyP.; The alphaalphabetabeta isomer of meso-tetrakis( N-(R)-(+)bornylacetamido-2-pyridyl)porphyrin (2-TRBorPyP), the major product obtained in its synthesis, was metallated with manganese(II) acetate under air to yield the manganese(III) porphyrin. The catalytic activity of this compound in the presence of various oxidants for enantioselective epoxidation of unfunctionalized olefins was studied in a mixture of water and acetonitrile at pH 7.4. The products were separated by chiral HPLC. The results indicated reasonable turnover numbers and modest enantioselective excesses.; Recognition of chiral small molecules such as amino acids, amines, and carboxylates with artificial receptors can give us useful information about host-guest interactions in biological systems. Furthermore, these receptors can be developed into chiral sensors. The binding of amino acids and amines with zinc(II) alphaalphabetabeta 2-TRBorPyP and another water-soluble chiral porphyrin zinc(II) alphaalphabetabeta meso-tetrakis( N-(R)-(+)-alpha-methylbenzylacetamido-2-pyridyl)porphyrin in aqueous solution was probed by UV-visible and fluorescence spectroscopy, and the results indicated chiral selectivity.